The present invention concerns electronic display devices and, in particular, a method for repairing tilemodules in large-area display devices that are formed as an array of tiled display devices.
There is an unmet need for large-area flat displays. No clear solution is apparent in the market place. This unmet need is becoming increasingly critical since the advancement of information results in increasing amounts of data to be displayed. A solution for large-area displays is needed to serve as the human interface for conveying information from sensors, computers, databases, cameras, etc. in this information dominated age. Many critical applications demand large-area displays:                Home theater applications        Applications that require multiple viewers        Applications in which the user needs to move about in an area        Applications where simulation of the real world is needed for training.        
The requirements for each application differs in size, shape, total number of picture elements (pixels), and brightness. Requirements that are common to most applications include, a relatively large number of pixels, color, ruggedness, portability (minimum thickness and weight), reliability, low power, and affordable cost. A good display solution does not exist for these needs using present technology.
There are fundamental technical issues that impose scaling-laws and limit the complexity and size of displays that can be profitably manufactured. These fundamental limitations are one reason why a technical solution that meets the need for large-area displays has not been achieved.
One measure of the complexity of a display device is its total number of pixels. The evolution of display technology has made newer and more complex pixel formats possible—VGA, SVGA, XGA, and SXGA for instance. Increased complexity typically is accompanied by added costs. The underlying cause of this empirical complexity law is yield losses caused by random material or particle defects. These defects cause manufacturing yields to diminish as the number of pixels in the display increases.
The measure of size of the display is its area. Costs increase exponentially with size. Each technology, LCD, PDP, EL, etc., has its own limit on maximum size. The underlying technical cause of this empirical relationship is tolerance. It is desirable to hold tight tolerances in manufacturing displays because, as the size increases, the effects of thermal expansion, humidity, residual stresses, and physical sag become more important.
Building a large-area display out of smaller tiles has been recognized as a desirable solution. Tiling is an approach that provides great flexibility for size and shape. Tiling is not subject to many of the problems that limit the size of monolithic display technologies. The complexity law does not apply because, depending on the size of the tile, the basic unit of manufacture in tiled displays is less complex than a large, monolithic multipixel display. The size law is not a limiting factor because the basic unit of manufacture is relatively small. Tiled displays obey a scaling-law which is not exponential but linear with display area. This fundamentally different scaling behavior is one advantage of tile technology. It makes these displays possible and reduces manufacturing costs.
These same issues lead to a desire to provide a repair means for large-area display devices, particularly the issues of ruggedness, reliability and affordable price. The smaller the unit that must be replaced, or repaired, when a defect occurs, the less the expense incurred in the repair. Again tiling may provide-an answer, through the approach of modular repair. In a tiled display the individual tiles are desirably inexpensive, relatively, to manufacture. A system designed to allow for the replacement of an individual tile is, therefore, less expensive to repair. Also the expense of the repair would depend on the size and complexity of the individual tiles, not the size and complexity of the entire display, eliminating the scaling-law issue of large-area displays with regard to their repair.
One type of tiled display is disclosed in U.S. patent application Ser. No. 09/250,324 filed on Feb. 16, 1999, which is incorporated herein by reference for its teaching on tiled displays. This application describes an OLED display which is formed as tiles that may be joined together to provide a large-area display device.